There are known various testing methods for residual capacity and deterioration of an accumulator battery. For example, there is known a method in which residual capacity is measured by means of discharging completely an accumulator battery, and the deterioration is determined with use of the residual capacity. However it is difficult to apply this method to an active accumulator battery hooked up with loads because it is necessary to completely discharge the accumulator battery, and moreover the method is not suitable for practical usage due to a long measuring time. So there has been developed a method which enables to immediately determine the deterioration of an active accumulator battery.
For example, under the condition that the temperature of an active accumulator battery varies, there is known a method in which voltage and temperature of an accumulator battery are measured, and the deterioration of the accumulator battery is determined by means of the conversion of the measured voltage at the measured temperature into the voltage at a specified temperature (cf. JP2001-185233A).
Furthermore, as for such secondary battery as a lead storage battery mounted in a car, a technique for measuring internal impedances of the secondary battery is proposed (cf., for example, JP10-056744A). In general, since it is possible to determine the deterioration of a secondary battery with the use of measured internal impedances of a secondary battery, the above-mentioned technique is very important. The current flowing through a secondary battery and the voltage due to the flow of the current are measured under the condition that the secondary battery is neither charged nor discharged, and then it is possible to calculate internal impedances of the secondary battery from the measured current values and the voltage values.
In the specification of the above JP10-056744A, as a method for measuring internal impedances of a secondary battery, there is proposed a method in which discharge currents with a constant frequency are applied to the secondary battery, and the internal impedances are calculated by means of Fourier transformation of the discharge current waveforms and the voltages waveforms responsive to the discharge currents. Such a method as described above makes it possible to calculate internal impedances with relative high accuracy so that it is possible to precisely determine the deterioration of the secondary battery.
Furthermore, as for such secondary battery as a lead storage battery mounted in a car, there is known a technique for determining deterioration of the secondary battery (cf., for example, JP2001-228226A). Since internal impedances of a secondary battery in general correlate strongly with deterioration level of the secondary battery, it is possible to determine the degradation of a secondary battery from the results of the internal impedance measurement of the secondary battery. Thereby, it is possible to encourage users to replace some secondary batteries with high deterioration level. It is necessary to employ the system in which there are measured current values and voltage values of a secondary battery due to flowing predetermined currents through the secondary battery and there are calculated the internal impedances by means of predetermined process, so that the power supply system has the function of determining the deterioration of the secondary battery.
Furthermore, as for a sealed lead storage battery, there is known a technique for calculating internal impedances from discharge currents and terminal voltages of the battery due to the discharge (cf., for example, JP9-232005A). In general, when discharge currents at a predetermined frequency are flowed due to discharge of a sealed lead storage battery at the predetermined frequency, current values and voltage values at a given frequency are calculated respectively from discharge current waveforms and discharge voltage waveform by means of Fourier transformation with the predetermined frequency as a basic frequency, and the internal impedances of the battery are calculated by means of dividing the voltage values by the current values.
When secondary battery is used in an outdoor station where an observation equipment or communication equipment is set up, or when secondary battery is mounted in a car, broad zones and various use environments should generally be considered, and therefore it is important to assure normal use of the secondary battery over a wide range of temperature. In the meanwhile, internal impedance significantly changes depending on temperature, and in particular the lower temperature it is, the larger internal impedance grows. Therefore even though the internal impedance of a secondary battery is within the allowable range at ordinary temperature, it may be difficult to use the secondary battery at low temperature. So when the deterioration of the secondary battery is unfailingly determined, it is necessary to calculate internal impedances with temperature correction in any way.